1. Field of the Invention
The present invention relates to a method of manufacturing a disk substrate made of semiconductor, glass, or the like.
2. Description of the Related Art
In recent years, compact information terminal devices, such as cell-phones or portable music players, including a high-capacity hard disk drive have been developed. There is a need to increase a capacity of a magnetic disk that is a recording medium used in a hard disk drive and to reduce a size of the magnetic disk. To meet such a need, a glass substrate has been used as a substrate of a magnetic disk used in a hard disk drive instead of a conventional aluminum alloy substrate. Furthermore, such substrates are generally used in, for example, silicon monocrystal wafers that are used in manufacturing semiconductor devices.
A glass substrate used in the above applications is formed into a circular shape (a disk), or a circular shape having a circular hole at its center. However, inner and outer edges of the glass substrate can be easily damaged due to an internal stress or an external factor such as a physical contact. Therefore, a chamfering process is performed on the glass substrate to chamfer the inner and outer edges of the glass substrate. For example, Japanese Patent Application Laid-open No. 2003-231044 discloses such a processing technology for chamfering a glass substrate.
In Japanese Patent Application Laid-open No. 2003-231044, as shown in FIG. 10, a disk-shaped glass substrate 6 having a circular hole at its center is rotated, and an outer end surface 63 and an inner end surface 64 of the glass substrate 6 are pressed against outer surfaces of cylindrical rotary grindstones 71, 72. As shown in FIG. 11, a plurality of grinding grooves 71a is formed over the entire outer surfaces of the rotary grindstones 71, 72. A tapered surface 71b is formed on the grinding groove 71a such that a width of the grinding groove 71a becomes narrower toward the inner side of the grinding groove 71a. Abrasive grain, such as diamond abrasive grain, is adhered on the inner surface of the grinding groove 71a. The tapered surfaces 71b of the grinding grooves 71a make contact with the outer end surface 63 and the inner end surface 64 of the glass substrate 6, so that the inner end surface and the outer end surface are ground, and the edge portions are chamfered. Moreover, a chamfering process is performed using the same configuration in a method of beveling a wafer disclosed in Japanese Patent Application Laid-open No. H9-181021.
However, in the conventional chamfering method, as shown in FIG. 11, a portion a that is in contact with the edge portion of the glass substrate 6 is intensively worn by friction with the edge portion. As a result, a continuous concave line is formed over the whole circumference of the tapered surface 71b of the grinding groove 71a of the rotary grindstone 71. Every time such a line is formed on the tapered surface 71b, it is necessary to change the grinding groove 71a used for grinding the glass substrate 6 to the grinding groove 71a arranged at a lower level, or to perform dressing on the rotary grindstone 71. Thus, in the conventional chamfering method, maintenance of the grindstone is considerably time consuming. Moreover, in the conventional chamfering method, there is a problem that chipping can easily occur on a chamfered portion and a main surface of the glass substrate 6, and scratches can be easily formed in a stripe pattern on a chamfered portion formed by grinding. Especially, because a glass substrate to be used as an information recording medium needs to be processed with an extremely high precision, a failure to finish a ground surface or a boundary between a ground surface and a substrate surface has been a serious problem.